From plus-size models strutting the catwalks, to curvaceous superstars like Adele belting it out at the Oscars (and winning one for "Skyfall") and Lena Dunham proudly bearing it all in her hit HBO show, "Girls," plus-size is going mainstream.

Two-thirds of Americans are overweight or obese, and several clothing stores, like Fashion to Figure, are marketing cute clothes for bigger girls.

"I think in today's world, when there's so many positive role models out there, Octavia Spencer, Adele, Melissa McCarthy from 'Bridesmaids' and lots of people like that, I think, are changing the way things are viewed," said Fashion to Figure CEO Michael Kaplan. "And those biases hopefully will become removed over time."

Vogue, a magazine famous for featuring super-skinny figures, will soon feature Kate Upton, a swimsuit model known for her curves, on their cover.

So is there still real shame in being overweight? For the gym-goers at Downsize Fitness in Chicago, the answer is, "Yes."

At Downsize Fitness, membership is reserved for the overweight only -- those who are at least 50 pounds overweight -- because they feel "fat shamed."

"Before I came here, I did try to lose weight," said one gym-goer named Chris Almaguer. "But with me being my size, I would literally stay up all night, maybe around 4, 5 a.m., go outside just to walk so no one would see me."

"There is a need for a place that people, heavy people need to go an concentrate on losing weight," said David Lanz.

They are all self-described outcasts from the mainstream gym scene, where they often felt ostracized.

"There's not a culture of acceptance in America for overweight people," said Francis Wisniewski, co-founder of Downsize Fitness. "You can still make fun of it in movies. You can still discriminate against based on size. So it's still that last thing in America that you are not protected on."

Downsize Fitness is now part of the national argument: Are overweight people still treated differently?

Just this week, CVS Pharmacy told its employees they had to submit information on their weight, body fat and glucose levels or pay a "surcharge," an extra $600 per year, for the company's health insurance plan.

Another hot button question: Should overweight airline passengers have to buy an extra seat?

Blogger Kenlie Tiggerman said she was humiliated by a Southwest Airlines gate agent in 2011.

"The gate agent came up to me and he asked me how much I weighed, what size clothes I wore," she told "Nightline" in a 2012 interview. "He said that I was too fat to fly, that I would need an additional seat."

Sharon Robertson has also felt the pain of harsh stares and ridicule. She joined Downsize Fitness last year, when her starting weight was 376 pounds and she said she was still reeling from the sting of a bad experiences with a personal trainer at a mainstream gym.

"I don't know if she was afraid of training a fat person or what it was," Robertson said. "So all I was able to do was sit in a corner and work on a treadmill. It definitely hurt."

In six months at Downsize Fitness, Robertson dropped 20 pounds. Her goal weight is 225.